Resistance element and furnace containing the same



W. C. SEIFERT Filed April 9. 1956 Nov. 25, 1958 RESISTANCE ELEMENT AND FURNACE CONTAINING THE SAME W/LL /M C. SE/FERT BY olu ATTORNEY United States Patent O RESISTANCE ELEMENT AND FURNACE CONTAINING THE SAME William C. Seifert, Narberth, Pa., assigner to Donald W. Kent, Philadelphia, Pa.

Application April 9, 1956, Serial No. 577,128

2 Claims. (Cl. 201-66) This invention is a new and useful electrical resistance element of .the direct radiation type and furnace containing the same. The invention will be fully understood from the following description, read in conjunction with the drawings, in which:

Fig. 1 is a diagrammatic showing of one step in the manufacture of the element of my invention;

Fig. 2 is a diagrammatic showing of a second step in the manufacture of said element;

Fig. 3 is a longitudinal section through a furnace containing said electrical resistance element; and

Fig. 4 is a transverse section through the showing in Fig. 3 on the plane indicated by the line 4 4.

Referring to Fig. 1, the tube 1 is made of a metal resistant to gas phase corrosion. The exact composition will be determined by the atmosphere to be maintained in the furnace in which the eventual resistance element is installed. The following are examples of alloys which are suitable:

Nickel 80%-chrome 20% Nickel 72%-chrome 1li-17%, balance Fe Chrome 11-14% balance Fe Nickel 18% chrome 8% balance Fe The lower end of tube 1 is sealed by squeezed portion 2, kand the upper end is connected to hopper 3, provided with vibrator 4 and containing finely divided high-melting-point inorganic oxide, such as alumina, zirconia, or magnesia. By operating vibrator 4, tube 1 is completely filled with oxide. For certain critical uses this operation may be performed under vacuum. The other end of tube 1 is then sealed by squeezed portion 6 and engaged by gripper jaws 7, upon which traction is exerted by chain 8 to draw the tube through swaging die 9, secured in holder 11. The drawing reduces the external diameter without substantially affecting the wall thickness, thereby reducing the enclosed volume and compressing the contained oxide. The redu-ction is carried to the point at which the oxide has reached maximum density, i. e., at which the voids are substantially eliminated. This results in a current carrier, which is characterized by uniformity of thermal radiation combined with exceptional strength and rigidity at extremely high temperatures. It is easily formed by mechanical deformation into loops, festoons, or other special shapes for special purposes, which retain their form even at temperatures in excess of 2000 F.

in Figs. 3 Iand 4, furnace or heating chamber 12 includes sides 13 and 14, bottom 15 and top 16 enclosing refractory inside walls 17 and 18, roof 19, and floor 20. The ends of the furnace define ports 21 and 22. Port 21 may be closed by door 23, consisting of steel frame 24, carrying refractory facing 25. The door may be lifted out of position by steel cables 27 and 28. Port 22 may be closed by door 29, consisting of steel frame 30, carrying refractory facing 31. Door 29 may be lifted out of position by cables, of which 32 is shown in Fig. 3.

The refractory inside wall 18 carries a series of projections 33, which may, for example, consist of a suitable refractory, such as bonded alumina or magnesia set in and projecting from the inside surfaces. The fully formed tube 1 is mechanically deformed into a series of loops 34, which are simply hung on these projections.

Refractory wall 17 also carries a similar series of projections 36, upon which a similar tube 37 is hung.

Each end of tube 1 is formed into a right-angle bend, which is carried through a hole 35 in one side wall 18 of the furnace and connected into an external electric circuit by which the heating current is provided. At this point the tube cross-section is reinforced with an external metal sleeve to lower its resistance. Temperatures obtaining in the furnace are measurable by thermocouple 40 in combination with any suitable recording instrument (not shown). Tube 37 is similarly formed into a rightangle bend, which is carried through hole 38 in the side wall 17 of the furnace.

Referring to Fig. 4, transformer 41 receives current through the primary connections 42 and 43 and supplies current through secondary posts 44 and 45. The end of tube 1 shown in the figure is electrically connected through lug 48, cable 47, and lug 46 with secondary post 44. The end of tube 37, shown in the figure, is electrically connected through lug 53, cable 52, and lug 51 with secondary post 44. The other ends of tubes 1 and 37 are similarly connected with post 45 -through similar cables and lugs. Y

In operation the tubes may, for example, be maintained at a temperature of about 2150 F. to hold the furnace interior within 50 F. of the resistor temperature. Owing to the construction, the furnace may conveniently be constructed to operate with a Vacuum or special atmosphere.

The resistors of my invention are characterized by extremely high uniformity of wall thickness and by circumferentially uniform radiation characteristics. They do not distort even at extremely high temperatures. They are free from the interference effects which obtain with ribbon-type resistors and show little or no tendency to creep at high temperatures.

I claim:

1. An electrical resistance element of the direct-radiation type, consisting of an external, tubular sheath of highmelting-point metal, resistant to gas-phase corrosion, surrounding a core of high-melting-point inorganic oxide and reduced in diameter upon said core by longitudinal extension to compress said core to maximum density.

2. An electric resistance element of the direct-radiation type, comprising an external tubular sheath of high-melting-point metal resistant to gas-phase corrosion, surrounding a core o-f high-melting-point inorganic oxide reduced in diameter upon said core to compress said core to maximum density, and means for electrically connecting the ends of said sheath to an external electric circuit.

References Cited in the file of this patent UNITED STATES PATENTS 493,314 Thomson Mar. 14, 1893 1,121,743 McClelland Dec. 22, 1914 1,359,400 Lightfoot Nov. 16, 1920 1,473,107 Kohn Nov. 6, 1923 1,731,119 Abbott et al. Oct. 8, 1929 1,861,947 Woodson et al. lune 7, 1932` FOREIGN PATENTS 11,128 Great Britain of 1908 268,795 Switzerland Sept. 16, 1950 

2. AN ELECTRIC RESISTANCE ELEMENT OF THE DIRECT-RADIATION TYPE, COMPRISING AN EXTERNAL TUBULAR SHEATH OF HIGH-MELTING-POINT METAL RESISTANT TO GAS-PHASE CORROSION, SURROUNDING A CORE OF HIGH-MELTING-POINT INORGANIC OXIDE REDUCED IN DIAMETER UPON SAID CORE TO COMPRESS SAID CORE TO MAXIMUM DENSITY, AND MEANS FOR ELECTRICALLY CONNECTING THE ENDS OF SAID SHEATH TO AN EXTERNAL ELECTRIC CIRCUIT. 